Life cycle responses of the midge of Chironomus species (Diptera: Chironomidae) to sugarcane and paper pulp effluents exposure

Abstract

The degradation of freshwater systems is on the increase due to anthropogenic activities. In the recent past, there has been a rapid shift of assessment and monitoring from the conventional methods to biomonitoring of these ecosystems globally. Although, an organism’s response to degradation varies, little is known as far as their sensitivities are concerned. The aim of this study, therefore, was to assess the life cycle responses of the midge of Chironomus species (Diptera: Chironomidae) to sugarcane and paper pulp effluents exposure. This is in order to ascertain their use in the monitoring of freshwater ecosystems. Fourth instar of Chironomid midges were sampled at two locations on the Rivers Nzoia and Mbogo. River Mbogo is a tributary joining River Nyando within the Lake Victoria Basin. All midges were taken to the laboratory on the same day of collection and acclimatized in a controlled climate room for 24 hours. They were then exposed to the effluent dilutions (i.e. 100%, 50%, 25%, 12.5% and lastly 6.25%) collected from Webuye Paper Mill Factory and Chemelil Sugar Factory treatment ponds/lagoons. A completely randomized experimental design was employed in which ten midges were placed in each of the treatments replicated four times and the experiment ran for 28 days. It was found that emergence of the Chironomus species decreased with an increase in the effluent concentration. An increase in effluent concentration, led to a delay in emergence of chironomids over time. However, there was no significant difference (p<0.05) between the emergence of Chironomus species exposed to the two effluents. Emergence is one of the most sensitive endpoints in toxicological studies. This is because effects on emergence involve three moultings and the very complex pupation process. Therefore, not all surviving larvae would have managed to undergo all the four stages of their life cycle due to adverse effects of the effluents. The study concluded that pulp paper and sugar cane effluents delayed the development of life cycle stages of Chironomus species and it was recommended that life cycle stages of the midges, Chironomus species can be a good indicator of environmental degradation.